Field of the Invention
The disclosed and claimed concept relates to a spray gun system utilizing a nozzle structured to dispense liquids, i.e. spray a liquid, and, more specifically, to a spray gun system including an air halo nozzle assembly for providing a gaseous barrier extending about a liquid flow stream.
Background Information
Certain fluid dispensing systems are structured to dispense a liquid such as, but not limited to, a sealant or an adhesive onto a substrate. The remainder of this description shall use an adhesive as an example, but it is understood that the liquid is not limited to an adhesive. Such liquid dispensing systems may utilize nozzle assemblies, or “spray guns” that are closed by an internal needle. Generally, an adhesive is either a solvent-based adhesive or a water-based adhesive. In some aspects, the spray gun is adapted to a specific type of adhesive. For example, a solvent-based system will include a temperature control to maintain the temperature of the liquid.
The spray gun includes a housing that defines a chamber with an exhaust passage, that is, a nozzle. The chamber includes a liquid inlet and may contain a liquid outlet. The liquid flows into the chamber via the liquid inlet. The liquid may be stored, briefly, in the chamber before application. For a water-based adhesive, the liquid is, typically, expelled exclusively via the nozzle. For a solvent based adhesive, a portion of the liquid may be dispensed via the nozzle and any excess liquid that may be recycled exits the chamber via the outlet. The liquid may then be drained from the system, or, reheated and re-circulated.
The nozzle defines an internal, elongated passage having a generally frusto-conical shape, i.e. a frustum. The nozzle further includes an internal seat; the seat may be part of the internal surface of the nozzle. A needle having its longitudinal axis aligned with the axis of the nozzle passage is used to seal the passage; that is, the needle coupled to an actuator structured to move the needle in an axial direction; i.e. longitudinally. The needle proximal end is coupled to the actuator and the opposite end of the needle distal tip is shaped generally, or substantially, to correspond to the shape of the nozzle seat. When the needle is in a forward, first position, the needle distal tip sealingly engages the nozzle seat. In this configuration, the spray gun is closed. When the needle is in a retracted, second position, the needle distal tip is fully spaced from the nozzle seat. In this configuration, the spray gun is open. Further, and as described below, the needle may also be placed anywhere between the first and second position, thereby causing the nozzle to be partially open. That is, when the needle is in the second position, i.e. fully spaced from the nozzle internal passage, the nozzle is, essentially, unblocked and allows for the nozzle's maximum flow rate. It is noted that, while in the second position, the needle may be disposed within the nozzle internal passage, so long as the nozzle achieves its maximum intended flow rate. If the needle is somewhere between the first and second positions, the nozzle is partially open and the liquid flows at a rate less than the maximum flow rate. Any time the nozzle is open, or partially open, the liquid forms a stream, or spray, between the nozzle and substrate. As used herein, the emerging liquid product is identified as a “flow stream.”
Typically, such spray guns must be opened and closed both rapidly and intermittently. That is, the nozzle is cyclically opened a brief period of time, then closed for a brief period of time. This would allow, for example, a quantity of sealant to be applied to an object while the spray gun is open, then for the object to be moved and replaced while the spray gun is closed. This is useful for an automated process or assembly line wherein objects such as, but not limited to, cans or shells are moved through the fluid dispensing system.
A disadvantage of such a system is that, when the flow stream of the compound is interrupted by the needle, the compound stretches then breaks. When it breaks, small pieces of compound are flung around the needle and nozzle. These particles eventually settle on the nozzle or other parts of the spray gun. That is, during application of the liquid, the air flowing about the shells and the machine carrying the shells, as well as the flow stream itself, creates a fluid flow pattern in the air disposed about the flow stream. The flow pattern of the air typically includes a vortex, i.e. air flow that rotates back toward the nozzle, and/or may be turbulent. The final portion of the stream of liquid, i.e. the last liquid out of the spray gun when the spray gun closes, breaks into particles and some of those particles are carried by the vortex or turbulent airflow back to the nozzle or onto other parts of the spray gun or nearby machine components. Hereinafter, and as used herein, the final portion of the stream of liquid that breaks into particles is identified as “snapback particles.” Over time, the snapback particles build up on the nozzle and other machine components and requires removal. Removal of the snapback particles requires the operation of the spray gun to be halted resulting in down time for the spray gun and machines.
There is, therefore, a need for a system to direct the snapback particles to the desired substrate. There is a further need for such a system to be compatible with existing fluid dispensing systems.